Sisk group is currently on site fitting-out the Shangri-La luxury hotel between floors 34 and 52 of the tower.
Fit-out work started in January 2012.
The hotel was originally due to open later this month with the first bookings being taken from April.
But Shangri-La has now told potential visitors on Twitter that it is “hoping to take bookings by early June” and September is now the earliest opening date.
The firm added: “We look forward to be able to communicate our confirmed opening date in due course.
“We want to make sure our product and services are completely ready.”